The long-range goal of this project is to make a significant contribution to the understanding of the chemical reactions involved in processing and storage of information in the central nervous system, i.e., in learning and memory. Current concepts of the mechanisms involved suggest that some long-lasting modification (structural, physiologic, and/or chemical) occurs as a direct result of environmental stimuli. The term "plastic changes" has been given to these modifications, and it has been possible for physiologists and anatomists to design experiments to detect such changes. This project proposes to determine whether it is possible to detect chemical modifications which can be correlated directly with the phenomena reported on by other disciplines. Our efforts have been directed toward understanding the synthesis, metabolism, storage, etc., of specific neurotransmitters in the central nervous system. For these studies, we have used the large, identifiable individual neurons of the marine mollusc, Aplysia californica, and have obtained information regarding the cell-specific distribution of various neurotransmitters. In addition, we are studying other chemical and metabolic properties that distinguish one nerve cell from another. It is quite possible that such cell-specific properties represent the molecular site which is modified by environmental stimuli. By studying the relationship between biochemical and physiological phenomena at the level of single neurons, we hope to be able eventually to describe chemical plasticity in terms of physiological changes.